The present disclosure relates to a developing device mounted in an image forming apparatus such as a copier, a facsimile, a printer, or the like, and the image forming apparatus including the same. In particular, the present disclosure relates to a developing device adapted to suppress aggregation and adhesion of developer and an image forming apparatus including the developing device.
Conventionally, as a developing method using dry toner in an image forming apparatus using an electrophotographic process, there are known a one-component developing method using one-component developer consisting of magnetic toner or non-magnetic toner and a two-component developing method using two-component developer for charging non-magnetic toner by magnetic carrier, in which a magnetic brush constituted of magnetic carrier and toner formed on a developing roller develops an electrostatic latent image on an image carrier (photoreceptor).
In the developing device described above, the toner is consumed by a developing operation. Therefore, a toner sensor for detecting toner density (or toner amount) is disposed in the developing device, and new toner is supplied in accordance with amount of toner consumed by developing. In this case, when charging amount of newly supplied toner is not sufficient, an image defect such as toner scattering or fog may occur. Therefore, in the two-component developing method, it is necessary to sufficiently agitate and mix the toner and the carrier so that the toner is charged to a predetermined charge amount. In addition, also in the one-component developing method, it is necessary to sufficiently mix the toner in the developing device with newly supplied toner so that charge amount distribution becomes uniform.
Therefore, there is a widely used method in which a circulation path of developer is disposed in the developing device, and an agitating feeding member having a screw shape constituted of a rotation shaft and a helical blade disposed in the circulation path agitates and mixes the developer so as to circulate and feed the same. Specifically, in a developing device 101 as illustrated in FIG. 18, an inside of a developing container 102 is divided into a first transport path 105 and a second transport path 107 by a partition wall 103. A first spiral 109 and a second spiral 110 for mixing, agitating, and feeding the developer are disposed in a rotatable manner in the first transport path 105 and in the second transport path 107.
Then, the developer is agitated and transported in an axis direction (directions of arrow A1 and arrow A2 in FIG. 18) by the first spiral 109 and the second spiral 110, and is circulated between the first transport path 105 and the second transport path 107 via developer delivery portions 111a and 111b formed on both ends of the partition wall 103. In other words, the first transport path 105, the second transport path 107, and the developer delivery portions 111a and 111b form the circulation path of the developer in the developing container 102.
Here, as higher image forming speed is required in recent years, it has become necessary to increase also a circulation speed (feed speed) of the developer in the developing device. As a method of increasing the feed speed of the developer, there is usually a method of increasing rotation speed of the first spiral 109 and the second spiral 110 illustrated in FIG. 18 and a method of increasing a pitch of the helical blade, for example.